Add an way to include the Microsoft standard "Press F1 for help" to screentips in the ribbon, including the behavior to perform an action when the F1 key is pressed.
UPDATE: The RibbonView exposes a HelpCommand property which basically sets the Help button command. Additionally the Help button has a predefined ScreenTip which content is controlled by the “RibbonViewHelp” resource key. You can easily change the value returned by the ResourceManager for that resource key to change the default ScreenTip information.
As for performing a custom action on F1, this is considered application logic which can easily be implemented through InputBindings (http://msdn.microsoft.com/en-us/library/system.windows.uielement.inputbindings%28v=vs.110%29.aspx).